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Register a new userMeasurement of $J/psitogammaeta_{rm c}$ decay rate and $eta_{rm c}$ parameters at KEDR
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Using the inclusive photon spectrum based on a data sample collected at the $J/psi$ peak with the KEDR detector at the VEPP-4M $e^+e^-$ collider, we measured the rate of the radiative decay $J/psitogammaeta_{rm c}$ as well as $eta_{rm c}$ mass and width. Taking into account an asymmetric photon lineshape we obtained $Gamma^0_{gammaeta_{rm c}}=2.98pm0.18 phantom{|}^{+0.15}_{-0.33}$ keV, $M_{eta_{rm c}} = 2983.5 pm 1.4 phantom{|}^{+1.6}_{-3.6}$ MeV/$c^2$, $Gamma_{eta_{rm c}} = 27.2 pm 3.1 phantom{|}^{+5.4}_{-2.6}$ MeV.
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We study $eta_{rm c}$ production at center-of-mass energies $sqrt{s}$ from 4.18 to 4.60 GeV in $e^+e^-$ annihilation data collected with the BESIII detector operating at the BEPCII storage ring, corresponding to 7.3 fb$^{-1}$ of integrated luminosity. We measure the cross sections of the three different exclusive reactions $e^+e^-rightarrow eta_{rm c}pi^+ pi^-pi^0$, $e^+e^- rightarrow eta_{rm c}pi^+ pi^-$, and $e^+e^- rightarrow eta_{rm c}pi^0gamma$. We find significant $eta_{rm c}$ production in $e^+e^-rightarrow eta_{rm c}pi^+ pi^-pi^0$ at $sqrt{s}$ of 4.23 GeV and 4.26 GeV and observe a significant energy-dependent Born cross section that we measure to be consistent with the production via the intermediate $Y(4260)$ resonance. In addition, we perform a search for a charmonium-like $Z_{rm c}$ state close to the $Dbar{D}$ threshold that decays to $eta_{rm c}pi$, involving ground state charmonium, and observe no signal. Corresponding upper limits on the cross section of $eta_{rm c}$ and $Z_{rm c}$ production are provided, where the yields are not found to be significant.
In this paper, we investigate the inclusive diffractive hadroproduction for $rm eta_{c}$ and $rm eta_{b}$ at the LHC energies. Based on the NRQCD factorization formalism and the resolved-Pomeron model for the quarkonium production mechanism, we estimate the rapidity, momentum fraction loss dependence of the cross section. We give prediction ratios for single and central diffractive processes with respect to non diffractive process. These inclusive processes are sensitive to gluon content of Pomeron for small-$x$ and Reggeon for large-$x$, useful to study small and large-$x$ physics and good to test different mechanism for $rm eta_{c}$ and $rm eta_{b}$ production at the LHC. They also serve as the background to related exclusive processes thus should be predicted. Our results demonstrate that the Reggeon contribution of diffractive processes can be sizable, even sometimes dominant over Pomeron, and that its study can be useful to better constrain the Reggeon parton content. The experimental study of Reggeon can be carried out in certain kinematic windows.
The decay of $J/psi$ to three photons is studied using $psi(3686)topi^+pi^-J/psi$ in a sample of $1.0641times10^8$ $psi(3686)$ events collected with the BESIII detector. Evidence of the direct decay of $eta_c$ to two photons, $eta_ctogammagamma$, is reported, and the product branching fraction is determined to be $mathcal{B}(J/psitogammaeta_c,eta_cto gammagamma)=(4.5pm1.2pm0.6)times10^{-6}$, where the first error is statistical and the second is systematic. The branching fraction for $J/psito3gamma$ is measured to be $(11.3pm1.8pm2.0)times 10^{-6}$ with improved precision.
In this paper, the inclusive Pomeron-Pomeron, Reggeon-Reggeon, Pomeron-Reggeon as well as gluon-Pomeron(-Reggeon) and photon-Pomeron(-Reggeon) interactions for the $rm eta_{c}$ at the LHC energies have been examined in proton-proton, proton-nucleus and nucleus-nucleus collision modes. The cross section has been computed based on the NRQCD factorization and Regge theory formalism. The cross exchange of Pomeron-Reggeon contribution is important in $rm pp$ and $rm pA$ modes. The Pomeron-Pomeron contribution is significant in $rm AA$ mode. The Pomeron contribution is considerable for $rm AA$ and $rm pA$ modes in single diffractive process where $rm A$ undergoes the diffractive process. Reggeon contribution is sizable in $rm pp$ and $rm pA$ modes where $rm p$ only undergoes the diffractive process. The Pomeron and Reggeon contributions in photon-Pomeron and-Reggeon process remain smaller than that of gluon-Pomeron and-Reggeon processes. Our results show that the experimental study of Reggeon, Pomeron and their cross exchange can be carried out in certain kinematic windows with the specific choice of the mode at the LHC. The investigation can be useful to better constrain the Reggeon and Pomeron parton content. The inclusive process serves as the background to related exclusive processes which should be predicted.
We search for $J/psi$ radiative decays into a weakly interacting neutral particle, namely an invisible particle, using the $J/psi$ produced through the process $psi(3686)topi^+pi^-J/psi$ in a data sample of $(448.1pm2.9)times 10^6$ $psi(3686)$ decays collected by the BESIII detector at BEPCII. No significant signal is observed. Using a modified frequentist method, upper limits on the branching fractions are set under different assumptions of invisible particle masses up to 1.2 $mathrm{ Gekern -0.1em V}/c^2$. The upper limit corresponding to an invisible particle with zero mass is 7.0$times 10^{-7}$ at the 90% confidence level.
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